My PC graphic setup comprises an A6-3500 APU and a Radeon HD 6770 1GB GDDR5 GPU. The PC is connected to a Samsung TV through the 6670 HDMI port; the GPU is configured to be the primary graphic card in the BIOS (the motherboard is an ASROCK A75M BIOS v2.00) and this is confirmed also by the Catalyst Control Center. Dual Graphics is also enabled both in the BIOS and in CCC. I then decided to use AMD System Monitor to made some tests.

As you can see from the graphic below, when playing a video game, the 6670 starts to work and sometimes, when needed, the 6530D of the APU works as a supplmentary computational capacity (this is not anyway captured below but I have checked it):

So, the Dual Graphics works as expected, considering the 6670 as the primary card.

I have then tried to play a 4K video (125 Mbps) and I was expecting to see the 6670 start to work as well...As you can see from the image below, only the CPUs were used and both GPUs (6670 and 6530D) utilization was 0%. The result was a heavy stuttering playback...

Just let you know that I was using MPC-HC player with LAV filters and DVXA2 (native) configured to be used also for 4K videos.

Finally the question: is this a correct behaviour? For video playback only the CPU are used? If yes, I'm quite confused to understand the DXVA2 concept...video should be decoded by the GPU...isn't it?